Diesel fuel for over-road use is taxed at a higher level (the “fuel tax”) than off-road use petroleum products such as agricultural/marine diesel and heating oil. These latter products are typically marked with dyes to distinguish them from over-road diesel fuel. The typical method to detect use of dyed products for over-road use is visual inspection, which can only be applied to a small fraction of the fuel sold for, and used in, over-road transportation. There also exist numerous methods to evade paying the fuel tax, and it is often suspected that fuel purchased in a state with a particular fuel tax is actually meant for use in a nearby higher-tax state. These schemes and this misdirection of fuel can often only be detected in hindsight and can be difficult to prove, leading to significant losses of revenue.